This invention relates to resid hydrotreating and, more particularly, to a process for increasing the conversion of 1,000+.degree.F. resid in a resid hydrotreating unit.
In the past, spiraling oil costs, extensive price fluctuations, and artificial output limitations by the cartel of oil producing countries (OPEC) have created instability and uncertainty for net oil consuming countries, such as the United States, to attain adequate supplies of high-quality, low-sulfur, petroleum crude oil (sweet crude) from Saudi Arabia, Nigeria, Norway, and other countries at reasonable prices for conversion into gasoline, fuel oil, and petrochemical feedstocks. In an effort to stabilize the supply and availability of crude oil at reasonable prices, Amoco Oil Company has developed, constructed, and commercialized extensive, multimillion dollar refinery projects under the Second Crude Replacement Program (CRP II) to process poorer quality, high-sulfur, petroleum crude oil (sour crude) and demetalate, desulfurize, and hydrocrack resid to produce high-value products, such as gasoline, distillates, catalytic cracker feed, metallurgical coke, and petrochemical feedstocks. The Crude Replacement Program is of great benefit to the oil-consuming nations by providing for the availability of adequate supplies of gasoline and other petroleum products at reasonable prices while protecting the downstream operations of refining companies.
During resid hydrotreating, such as under Amoco Company's Crude Replacement Program, resid oil (resid) is upgraded with hydrogen and a hydrotreating catalyst in a three-phase equilibrium of oil, catalyst, and gas bubbles to produce more valuable lower-boiling liquid products. In order to increase the efficiency, effectiveness, and profitability of resid hydrotreating, it is desirable to maximize the conversion of resid to more valuable lower-boiling liquid products.
Over the years, a variety of methods for processing resid with recycle oil have been suggested. Typifying some of the prior art methods for processing resid and other feedstocks with recycle oil are those found in U.S. Pat. Nos. 3,549,517; 3,681,231; 3,660,270; 4,457,831; and 4,411,768. Such prior art methods often use coke precursor absorption units to remove solids in the recycle oil or an extraction unit to remove propane or butane from the recycle oil. Such equipment can be expensive. Often prior art methods recycle some of the effluent directly from the reactor without removing light hydrocarbon gases or use vacuum oil. These prior art methods have met with varying degrees of success.
It is, therefore, desirable to provide an improved hydrotreating process for increasing the conversion of resid.